Ballpoint pen



March 31, 1970 HARUO KUBQTA ETAL 3,503,692

BALLPOINT PEN Filed Nov. 17, 1965 2 Sheets-Sheet 1 .SINK/NG' OF THE Pom/r B444 6 rH 0F 7H6 ZINE EL 9. Z (a) 7);) 1 WC- 6 7560 a? SINK/HG 51 OF THE PamrfiAu 1 ENG rH OF THE I: L wE SINK/M6 OF THE P0141154 NVE 1000 2000 l/maokaaarn Ina/ 4H: $2923,

LENGTH OF THE lav/4 LIME fulfil/x0001 HALSH/N/SH/MWA (Aka rHEes J Oreo rHEES THE/e Ar ram/E vs United States Patent 3,503,692 BALLPOINT PEN Haruo Kubota, Nishinomiya, Ryuichi Ishida, Sakai, Yoshihiko Doi, Tsuneyoshi Amagasaki, and Takeshi Nisikawa, Itami, Japan, assignors to Sumitomo Electric Industries, Ltd., Higashi-ku, Osaka, Japan, a company of Japan Filed Nov. 17, 1965, Ser. No. 508,227 Claims priority, application Japan, Nov. 21, 1964, 39/ 65,623 Int. Cl. B43k 7/10 US. Cl. 401215 4 Claims ABSTRACT OF THE DISCLOSURE W'C-Co cemented carbides or a cermet are used as the material for point balls in ballpoint pens. In the case of WC-Co cemented carbides, the carbon content is at or below 6.12% with excess tungsten dissolved in the Cophase or with the y-phase appearing in the WC base. In the case of a cermet, one or more carbides from the group Cr C TaC, NbC, WC and TiC is added to the cermet and bound together by means of nickel or nickel alloy.

This invention relates in general to an improvement of ballpoint pens and more particularly to an improvement in the point ball of ballpoint pens.

An object of this invention is to provide an improved ballpoint pen having an unusually long service life and being capable of assuring a clean and uniform inked line of unusually large total length drawn with the ball point at a very light touch of the point ball, without any Writing difficulty as in the case of unsmooth ink feeding, which results in lack of perfect integrity of a continuous clean inked line found in so many of the pens of ballpoint type.

Another object of this invention is to provide a novel point ball for a ballpoint pen having an unusually large wear resistance and accordingly being assured of an extraordinarily long service life as expressed by the maximum total length of a clean inked line that can be drawn at a light touch of the pen point.

Still another object of this invention is to provide a unique method of producing the above mentioned novel point ball.

Prior commercially available ballpoint pens are subject to definite writing disadvantages, such as blurring of the inked line drawn by the-pen, and also have a relative short service life in comparison with earlier fountain pens having a gold point, caused from the early Wear of the point ball.

This invention is directed to the removal of the second of the above described disadvantages inherent to the conventional ballpoint pens; the inventors have succeeded in finding the following fact from a series of researches on the corrosion mechanism of a hard alloy of the WC-Co type.

A point ball of a ballpoint pen in use will sufier from the gradual loss of only the Co-phase With WC-Co alloy employed as point ball material resulting from mechanical wear, which in turn gives rise to the subsequent removal of the WC originally bound by the C0phase. This eventually results in wear of a tip of the ballpoint pen holder thus causing a progressive apparent sink of the point ball within the holder which in turn is a cause of the unsmooth rolling of ball and eventual interruption of smooth ink feeding, beyond the tolerance for a clean drawn line, ultimately resulting in an early ending of the pens practical useful life. The early ending of the pens life may perhaps be attributable primarily to a relative low hardness of the Co-phase in comparison with the WC phase as well as the corrosion of the Cophase either by the chemical attack of chlorine, sulphur or other corrosive elements originally contained in the paper tissue upon which the pen is used and then picked up dissolved into the liquid ink, or by the oxygen dis solved in the ink, or possibly by galvanic action due to a potential difference between noble WC and less noble Co.

This invention is directed to a use of WC-Co type hard alloy and a new cermet containing bound carbide of metal, both having excellent characteristics for use as point ball material.

First reference is made to the WC-Co type hard alloy;

WC-Co type belongs to a hard alloy usually having the theoretical carbon content in tungsten carbide of C/WC=l2/(l84+l2)=6.12% at which no free carbon can be present in the alloy, and where free carbon can appear only When C/WC is in excess of 6.12%. Carbon content in WC phase below 6.12% means a presence of excessive tungsten, component which in turn becomes dissolved in the Co phase which is used as a metal binder for WC.

Quantitative solid solution of the excessive tungsten in the Co-phase is approximately 10%. The lower the carbon content, the larger the relative content of excess tungsten becomes, and, finally, the y-phase (alias fi-phase) of double carbide, as expressed by Co W C appears.

Prior commercially available hard alloys used to produce a cutting tool, wear resisting tool or the like, have a quantitative C content almost equal to the theoretical level. This has urged the development of a new hard alloy having an extremely low content of free carbon and free from the presence of above mentioned fi-phase. Any hard alloy of cemented carbide type containing the 6- phase or free carbon in excess of 0.1% is considered to be rejected as being unacceptable for use as a material for an excellent hard alloy tool.

The present invention is successful in confirming that WC-Co type hard alloy having the ii-phase, earlier mentioned as being generally unacceptable in use for making a cutting tool, is extremely suitable for use as a material for the point ball of a ballpoint pen, for which the hard alloy of the WC-Co type is assured of a favorable performance.

Principally, WC-Co hard alloy containing the B-phase can assure, when used as a point ball of the ballpoint pen, as much as 3 to 4 times the extended service life of the pen.

This is confirmed from the results of a series of experiments and testing conducted by the inventors for many point balls comprising of the WC-Co type hard alloys with diiferent selected contents of carbon so that the useful life of the point ball can be extended as soon as the C/WC value (C content) has been reduced down to and below 6.12% and, accordingly, W has been first dissolved in the Co-phase, and is thus, substantially stabilized for long service before the first appearance of the y-phase as can be readily seen from Table 1 and FIG. 1 of the present application.

A fuller understanding of the advantages offered by this invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings and tables, in which:

FIG. 1 shows a graphical representation of the relation of the sinking of the point ball within the tip of the ball holder of the pen and the corresponding total length of a continuous inked line providing a means of ready comparison between two different point balls, one in pursuant to an embodiment of this invention and another of a conventional type.

FIG. 2 is a graphical representation of the sinking of point ball against the corresponding total length of a continuous inked line representing the results of a writing test and providing a means of ready comparison between two different point balls, one in pursuant to another embodiment of this invention (made of cermet) and another of a conventional type.

FIG. 3 shows the graphical relation between the total length of a continuous inked line drawn with individual tested ballpoint pens one of the present invention and another of the conventional type, and the corresponding quantity of consumed ink.

FIG. 4 illustrates a sectional view of the enlarged model of the point ball in accordance with still another embodiment of this invention wherein the point ball made of WC-Co alloy having the y-phase on its surface.

FIGS. 5 and 6 are diagrammatic representation of the relation between the sinking of the point ball, as illustrated in FIG. 4 and the corresponding quantity of consumed ink.

In Table 1 there is listed the results of the point ball testings. A1 and A2 represent the point balls made of the conventional hard alloys and A3 to A6 present other point balls made of the new hard alloy in pursuant to the present invention.

In FIG. 1, the ordinate gives the sinking in millimeters of point ball and the abscissa set forth the total length of a continuous inked line in meters.

All the point ball testings results of which are listed in Table 1 and plotted in FIG. 1, were conducted by applying a load of 200 gr. on the point ball. It has been found from these experiments that the point ball pen becomes nonusable when the sinking of ball has achieved 0.1 mm.

TABLE 1 Free 0 Max. total Defiective C [W 0 percent length (inked strength, percent y-phase line) (m.) (kg/mmfl) 6. 20 0. 06 500 140 6. 14 0.00 1,000 150 6. 09 0. 00 2, 000 130 6. 00 Tracc 2, 000 120 5. 90 Trace 2, 000 80 5. 50 Trace 2, 000 60 All the point balls listed in Table 1 were tested under application of 200 gr. load. The ball holder is made of brass. The C/WC value was determined through chemical analysis. 72,000 m. and 1,200 m. in the column headed max. total length (inked line) show the max. total length of a continuous drawn line as determined not by wear of point ball beyond tolerance, but by the termination of ink feeding due to exhaustion, so that the listed value would have been larger, if the ink had lasted longer.

The content of carbon causing initial appearance of the y-phase in the hard alloy can not be expressed definitely, because it is always dependent on the content of Co, but may be given by the following empirical formula, considering excessive W which can be dissolved in Co-phase up to 10%.

C/WC (percent) g6. l2'y where a stands for a carbon reduction needed for causing the initiation of the appearance of the y-phase, (on may be deemed to be 0.006XCO) C/WC (percent) content having achieved 4, W C is then caused to initially appear which in turn is a cause of a drop in the mechanical strength of the alloy, rendering the alloy highly susceptible to cracking. The experiments conducted have produced the results so that percentage of C/WC of all tested point balls was above 5.

Another series of 200 gr. load testing experiments of point balls made of WC-TaC-Co type alloy and WC-TiC-Tac (or NbC)-Co type alloy, besides the above mentioned WC-Co type alloy, with the results as listed in Table 2 and Table 3 similar to those listed in Table 1. Applicability of other embodiments of the present invention has been confirmed with respect to other hard alloys of WC-Co type but containing HfC, ZrC and the like.

TABLE 2.WO2% TaC-5% Co ALLOY TABLE 3. WG-13 TiC-3 'IaC (or NbC)-9 Co ALLOY Max. total length (inked line) (m.)

Free 0 percent fi-phase Total 0 percent found The inventors also have found that besides the WC-Co type alloy containing the y-phase, the conventional WC-Co type alloy used for manufacture of the conventional pen of ball point type and another alloy, a variant of the WC-Co type containing additionally one or more of such carbide as TaC, TiC, NbC, HfC and ZrC, also can be provided with an adequate performance equivalent to that of the new hard alloy in pursuant to this invention above described, only if the conventional alloys have been so prepared that they are coated, either totally and partially, with the y-phase, that is, the y-phase is allowed to exist on the surface of the alloy.

FIG. 4 illustrates the cross sectional view of the enlarged model of the point ball made of the y-phase coated type hard alloy, and represents an embodiment of the present invention. The y-phase 12 is a coating on the surface of the ball 11, and can be seen as a black zone when observed with a microscope of about X200 magnification. The ball 11 shows a conventionally accepted microscopic structure of the inside of the WC-Co alloy base and can be seen to the white when viewed by means of the microscope for confirmation of the presence and pattern thereof.

Method of establishing this y-phase (12), coating the surface of the above described base alloy, is as follows. The hard alloy ball 11 of WC-Co type is first buried in the bed of alumina (A1 0 powder and then, while in the bed of alumina, is heated up to and held at a temperature of 1,000 C. to 1,300 C. for a continuous period from 10 minutes to 5 hours, in the atmosphere of hydrogen gas. The surface coating of the y-phase of the hard alloy of WC-Co cemented carbide type is composed of a double carbide of Co, W and C which is produced when the carbon content in the hard alloy is not sufficient to produce a compound from WC and Co. It is believed that the structure of the said y-phase may be built up, layer by layer, by W Co C, W Co C and other similar compounds.

The point ball, made of the new hard alloy pursuant to this embodiment of this invention, was tested for comparance with the conventional hard alloy balls, with special regard to the correlation of the ball sinking due to wear with the quantity of ink consumption when in position at the pen point of the ballpoint pen, with the results graphically illustrated in FIG. 5. In FIG. 5 the relation between the sinking of the point ball and the corresponding total'length of the continuous inked line is illustrated by curve A for the conventional ball and by curve B for a ball made of the new hard alloy in accordance with the above described embodiment of this invention. The curve A indicates a service life of the conventional ball as short as 500 m. expressed in the terms of the max. total length of continuous inked line because of the early wear of the point ball, while the latter curve B indicates an unusually small sinking of only about 0.03 mm. of the ball within the tip of the ball holder even after achieving a continuous inked line, a total length of 1,000 m., which means an additional as well as ample life of the tested pen having the new point ball prepared in accordance with this invention. In FIG. 6 there is shown the relation between the quantity of ink consumption and the corresponding total length of the continuous inked line produced as illustrated by curve A for the conventional ball and by curve B for the ball made of a new alloy in accordance with the above described embodiment of this invention. The former curve A indicates a peak of ink consumption corresponding to the total length of continuous inked line of only 200 m. and a subsequent drop as shown in this curve until about 400 m. is reached where the tested ballpoint pen has been found no longer usable. The latter curve B indicates almost constant ink consumption until the total length of the continuous inked line of 1,000 m. is reached which shows additional as well as ample subsequent service and life of the tested pen having the new point ball prepared in accordance with this invention over conventional ballpoint pens.

Reason for this unusually excellent performance of the point ball embodying this invention may be reasonably deemed to be the same as that for the new alloy having the y-phase coating.

Another embodiment comprising this invention is directed to a point ball made of another new hard alloy of WC-Co type, not having the presence of the y-phase but having the excellent performance, nearly equal to the alloy having the presence of the y-phase.

This embodiment is concerned with a particular type of cermet wherein a particular carbide is bound by means of a particular metal binder.

As is already known, cermet is a co-sintered product made from the carbides, borides and oxides of a metal and the metal itself; the carbide may be TiC, ZrC, B C, WC or similar and boride be CrB, ZrB or similar and the oxide may be A1 0 BeO, ZrO ThO or the like. The typical known type of cermet is one obtained by application of the hot pressing method to the crystal grains of the metallic compounds as an aggregate and then adding such metals as Fi, Ni, Co, Cr, Cu or the like.

The cermet of this type has, however, been employed only for making highly heat-resisting materials used for the construction of high speed engines.

This embodiment has been established after successful confirmation from the experimental productions of different cermets as an aggregate of the crystal grain and, as a binder, the alloys containing a carbide preferably of Cr and Ti, etc., and Ni or Ni-containing alloys are most recommendable. The results of the experiments made by the inventors have revealed that the best performance of the alloy product can be obtained when the Cr C with or without TiC, WC and the like, is used as an aggregate and Ni or Ni-Cr type alloy, Ni-Cr-Co type alloy or Ni-Cu type alloy is employed as a binder.

The use of cermet for the ballpoint pen not only provides an unusually highly wearproof point ball, but also assures the ballpoint pen having the point ball made of cermet to have an exceptionally long service life with light use of the point ball.

Some of the examples of the cermet to be used for manufacturing the point ball in accordance with this invention are as listed below.

(B2) Cr C-WC-Ni (WC=2%, Ni=15% (B3) TiC-Cr-Co-Ni (Cr=4%, Co=4%, Ni=12%) (B4) TaC-Cr-Co-Ni (Cr=2%, Co=2%, Ni=6%) (B5) NbC-Cr-Co-Ni (Cr=2%, C0=2%, Ni=6%) (B6) WC-Cr-Ni (Cr=l.5%, Ni=8%) (B7) Cr C -TiC-TaC-WC-Cu (68: 101514;]112

Results of wear-proofness testing carried out for the point balls made of the cermet pursuant to this invention are as follows.

In FIG. 2, both curves (a) and (b) show the plotting of sinking in millimeters of ball against corresponding total length of continuous inked line in meters. In FIG. 3, there is shown the graphical correlation of the total length of the continuous inked line (abscissa) with the corresponding consumption (mg./ m.) of the ink (ordinate). The symbols B1 to B5 given to the individual curves indicate the sample number of the tested cermets listed above.

As may be readily understood from the foregoing, for every example embodying this invention, use of the point ball prepared in pursuant to this invention for manufacturing the ballpoint pen not only assures a drastic extension of service and life of the pen in comparison with conventional pens of the similar type having the point ball made of a known hard alloy of cemented carbide type, to say nothing of conventional steel, but also enables unusually smooth continuous writing with light touch and use of the point ball for a long period of service.

The point ball, prepared pursuant to this invention may be used in combination with a point ball holder made of any stainless steel, brass, plastic and any other suitable holder material.

What is claimed is:

1. In a ballpoint pen, a cemented carbide point ball of improved durability in the holder tip of the pen wherein during the useful life of the pen, the sinking of the point ball into the holder tip is substantially nonvariant and does not exceed 0.1 millimeter under a 200 gram load, said point ball comprising a sintered WC-Co cemented carbide as a metal base wherein the carbon content by weight is within a range of 5% to 6.12% with initial appearance of a double carbide expressed as Co W C as the carbon content approaches the lower limit of the carbon range, the content of carbon causing such initial appearance dependent upon the content by weight of Co and the following relationship C/WC (percent) 6.12-'y where 'y is the necessary reduction of carbon content needed to cause said initial appearance of the double carbide.

2. In the ballpoint pen of claim 1, wherein the point ball includes at least one of the carbides selected from the group consisting of Cr C TaC, TiC, NbC, HfC and ZrC are added thereto to form the sintered cemented carbide.

3. In the ballpoint pen of claim 2 wherein the point ball further includes as a binder an alloy selected from 7 8 the group consisting of Ni, Ni-Cr, Ni-Cr-Co and Ni-Cu. FOREIGN PATENTS 4. In the ballpoint pen of cla1m 1, wherein the point 471,571 6/1935 Great Britain ball comprises a co-sintered base metal conslstmg of a 503,995 Great Britain. cermet and a binder selected from an alloy group con- 763 409 Great Britain sisting of Ni, Ni-Cr, Ni-Cr-Co and Ni-Cu. 5

OTHER REFERENCES References cued Cemented Carbides, Swarzkopf & Kieffer, New UNITED STATES PATENTS York, The MacMillan Co., 1960, pp. 4-10, 7480, 188. 5:133:55 Z333 v ii IIIIIIIIIII 53213533 10 CARL QUARFORTH, Primary Examiner 2,167,516 7/1939 Kelley 29 182.7 A. J. STEINER, Assistant Examiner 2,198,343 4/1940 Kiefler 29182.7 3,000,087 9/1961 Dyer 29 1s2.s S. Cl- X-R.

3,303,825 2/1967 Shuman 29 1s2.7 9 -7, 8 -8 

